Synthesis method for solution with high grade chloramine

ABSTRACT

The present invention relates to a process for the preparation of high-grade chloramine by the action of commercial eau de Javelle of 100 chlorometric degrees on a solution of ammonia in the presence of ammonium chloride. According to this process, the chloramine is obtained having a content greater than or equal to 2 mol L −1 , that is to say, greater than or equal to 10.3%. The process can be carried out continuously or discontinuously.

The present application is a U.S. National Application filed under 35USC 371 of PCT/FR98/02081, filed Sep. 29, 1998 based upon Frenchapplication Serial No. 97.12109 filed Sep. 30, 1997.

The present invention relates to a process for the preparation ofhigh-grade chloramine by the action of commercial eau de Javelle of 100chlorometric degrees on a solution of ammonia in the presence ofammonium chloride. According to this process, the chloramine is obtainedhaving a content greater than or equal to 2 mol L⁻¹, that is to saygreater than or equal to 10.3%. The process can be carried outcontinuously or discontinuously. Besides its applications as ableaching, disinfecting and bactericidal agent, monochloramine is usedin numerous reactions as a synthesis intermediate. In particular, it isthe principal reagent in the synthesis of pharmaceutically valuablehydrazines by the Raschig process. For example, N-amino-2-methylindolineand N-amino-3-azabicyclo[3.3.0]octane are prepared by reacting NH₂Clwith 2-methylindoline and 3-azabicyclo[3.3.0]octane according to theprocesses described in patent Specifications EP 462 016 and EP 277 267.

That method of preparation is currently attracting a great deal ofinterest in view of the fact that it causes little pollution comparedwith the prior methods of preparation, which make use of N-nitrosocompounds. It does, however, have disadvantages associated with the lowhydrazine content of the reaction liquors, which generally does notexceed 2 to 4%. That limitation is linked principally to the fact thatthe reagents, and especially sodium hypochlorite, are highly diluted,necessitating complicated and onerous extraction procedures. As aresult, the momentary concentration of chloramine in the reactor doesnot, even in the best of cases, exceed 1 mol L⁻¹ (5.15%).

In view of the fact that NH₂Cl is highly unstable in aqueous solution,synthesis in a more concentrated medium has not been attempted. Itsinstability is linked to competition between hydrolysis andautocatalytic dismutation reactions, which result in rapid acidificationof the medium and in the preponderant formation of dichloramine andnitrogen chloride. In a non-buffered medium the degradation can rapidlyresult in the solution boiling. Obtaining a higher monochloramine titrerequires the use of a new reagent of a high chlorometric degree andresearch into appropriate operating conditions.

The present invention makes it possible to double, at least, the NH₂Cltitre by using solutions of eau de Javelle of the order of 100chlorometric degrees and employing conditions compatible with obtaininghigh-grade (H.G.) chloramine. This new process makes it possible,starting from an identical unit volume of hypochlorite, to double theproductivity in terms of hydrazine and to make savings in raw materialsand energy in the synthesis, reagent recycling and distillationprocedures.

Because oxidation of ammonia by sodium hypochlorite is an exothermicreaction, it must be carried out at low temperature in order to limitthe degradation reactions. It is therefore necessary to cool thereagents beforehand, prior to their injection. For example, for asolution of eau de Javelle of 48 chlorometric degrees (crystallisationpoint=−21.4° C.), the temperature inside the reactor must not be higherthan −5° C. That limit has to be lower for an NaOCl content that istwice as high. Unlike hypochlorite at 2.14 mol L⁻¹ (48° chl.), asolution of eau de Javelle of 100 chlorometric degrees crystallises in astirred medium at 14° C. Crystallisation nevertheless remains difficultunless initiated. In a still medium, therefore, a very clear delay incrystallisation is observed and it is thus possible to maintain H.G. eaude Javelle solutions in a single-phase medium for several hours at −20°C. in glass vessels. However, in spite of the solution having littletendency to crystallise, it is necessary in the case of continuousindustrial synthesis to use the H.G. eau de Javelle at approximately 14°C. in order to avoid possible caking in the pipework.

As in the process for the preparation of NH₂Cl starting from sodiumhypochlorite of 48 chlorometric degrees, it is necessary to introduceinto the ammonia-containing reagent an amount of an acceptor compoundthat is able to neutralise completely the hydroxyl ions formed in situby the reaction:

ClO⁻+NH₃→NH₂Cl+HO⁻

The acceptor may be an acid, a water-soluble acid salt or awater-soluble neutral salt. It is, however, preferable to use anammonium salt of the type (NH₄ ⁺)H⁺ _(β)A^((1+β)−) wherein β is 0 or 1and A is Cl, CO₃ or NO₃ so as to buffer the reaction medium atapproximately the pKa of NH⁺ ₄/NH₃, to eliminate the HO⁻ ions and tokeep the concentration of free ammonia constant:

NH₄ ⁺+HO⁻→NH₃+H₂O

Furthermore, the combined ammoniacal mixture must be cooled to wellbelow −10° C. so as to absorb the heat given off and to compensate forthe heating associated with the injection of the hypochlorite at atemperature above its crystallisation temperature. Under thoseconditions, the cooling effect introduced principally by the ammoniacalsolution avoids the use of eau de Javelle in a supercooled state andhence ensures synthesis in a homogeneous medium.

Those constraints require that new ammoniacal combinations having a lowcrystallisation point of from −20° C. to −30° C. be found. Thecomposition of those mixtures is determined by the content of thehypochlorite solutions. The latter have a titre of about 100chlorometric degrees, which means that, under normal conditions, oneliter releases 100 liters of chlorine under the action of hydrogenchloride. The molar concentration of NaOCl is then 4.46 mol L⁻¹. Unlikethe extracts of 48 chlorometric degrees, the NaCl and NaOCl titres arenot in equimolecular proportions.

To obtain quantitative yields, the conditions of synthesis must meet thefollowing criteria:

The H.G. eau de Javelle can be used in the supercooled state but, inorder to prevent any initiation of crystallisation, it is preferable toinject it at a temperature higher than or equal to 15° C. The H.G. eaude Javelle is relatively stable and loses, per 24 hours, approximately1.3 degrees at 17° C. or 0.47 degree at 10° C.

The overall content of Lewis acid must be sufficient to neutralise atleast 90% of the hydroxyl ions resulting from the NH₃/NaOCl reaction.

The pH must be maintained at from 10 to 12, preferably at approximately10.5.

The ratio [total ammonia]/[ClO⁻] must be from 2 to 5 (preferably 2.7) soas to stabilise the chloramine that is formed.

The crystallisation point of the (NH₄ ⁺)H⁺ _(β)A^((1+β)−)/NH₃/H₂Owherein β is 0 or 1 and A is Cl, CO₃ or NO₃ ternary mixture must be from−20 to −30° C. so as to offset the frigorific deficit associated withthe injection of the chlorinated reagent at T≧15° C. in the context ofsynthesis in a single-phase medium.

The temperature inside the reactor must be in the range from −5 to −20°C., preferably about −15° C.

A large number of acids (HCl, H₂SO₄, etc.), neutral salts (CaCl₂, MgCl₂,ZnSO₄, etc.) and acid salts (NaH₂PO₄, NH₄HCO₃, NH₄Cl, NH₄NO₃, etc.) maybe used in the synthesis of chloramine. A priori, certain of those areextremely interesting because they possess more than one acidfunctionality in the same molecule. On the other hand, very few aresoluble and precipitate below 0° C. At this stage, the ammonium saltsare the most advantageous since they exhibit greater solubility, whichincreases as the ammonia content of the medium increases.

Under the conditions of synthesis defined above, use of polythermaldiagrams involving the NH⁺ ₄ ion shows that the ammoniacal combinationsmeeting the above criteria require the use of ammonium nitrate :NH₃—NH₄Cl—NH₄NO₃—H₂O or NH₃—NH₄NO₃—H₂O. Those combination mixtures allowoperation in a homogeneous medium down to a temperature of −30° C. Inthe absence of NH₄NO₃, the preparation of the H.G. chloramine can becarried out only in batches. In fact, at the start of the reaction, afraction of the neutralisation salt is insoluble; the mixture thenbecomes rapidly homogeneous as a result of dilution and neutralisationof the HO⁻ ions.

Thus, according to the invention, the continuous preparation ofchloramine in a homogeneous medium must be carried out in the presenceof an ammoniacal combination based on ammonium nitrate (NH₃/(NH⁺₄)_(α)H⁺ _(β)A^((α+β)−)/NH₄NO₃/H₂O), wherein α is 0 or 1, β is 0 or 1,and A is Cl or CO₃ preferably NH₃/NH₄NO₃/H₂O or NH₃/NH₄Cl/NH₄NO₃/H₂O;the discontinuous preparation of chloramine must be carried out usingmixtures of the type NH₃/(NH₄ ⁺)H⁺ _(β)A^((1+β)−)/H₂O wherein β is 0 or1 and A is Cl, CO₃ or NO₃, preferably NH₃/NH₄Cl/H₂O, which may bepartially insoluble in the course of the addition of the chlorinatedreagent.

The following Examples illustrate the process of the invention carriedout discontinuously and continuously, without limiting it:

EXAMPLE I

The reaction is carried out in a cylindrical, double-wall reactor madefrom borosilicate glass maintained at −20° C. by circulation of athermostatic fluid. The ammoniacal solution has a titre of 7.2 mol L⁻¹for NH₃ and 4.76 mol L⁻¹ for NH₄Cl, which corresponds to the followingcomposition by weight: 12.1% NH₃, 25.2% NH₄Cl, 62.7% H₂O. 30 ml of thatmixture are then introduced into the vessel with stirring until thermalequilibrium is reached. The sodium hypochlorite solution (104.4chlorometric degrees; 4.64 mol L⁻¹), in the supercooled state, is thenpoured in at a regular rate (duration of addition 10 minutes) in such amanner that the temperature inside the reactor does not exceed −10° C.Since the point representing the ammoniacal mixture is located, at thestart of the reaction, within the liquid+NH₄Cl two-phase region of thediagram for the ternary composition NH₃—NH₄Cl—H₂O (isotherm −20° C.),29.3% of the initial amount of ammonium chloride are precipitated. Inthe course of the addition of NaOCl, the mixture rapidly becomeshomogeneous as a result of dilution and elimination of the hydroxylions. At the end of the reaction a chloramine solution is obtainedhaving a titre of 2.18 mol L⁻¹ (11.2%), which corresponds to a yield of98% relative to the hypochlorite. Under the conditions described in thisexperiment, the high-grade NH₂Cl solution formed is relatively stable at−20° C. and loses only 1.4% after 15 minutes.

EXAMPLE II

Carrying out the synthesis under the same conditions but without initialprecipitation of NH₄Cl (homogeneous medium) requires the ammoniumchloride content to be reduced. As the saturation curve for the ternarymixture shows, the NH₃ titre has to be increased (injection of gaseousNH₃) so as to dissolve NH₄Cl. Starting, for example, from a commercial32% ammonia solution, the maximum dissolved amount of NH₄Cl allowed bythe −20° C. isotherm corresponds to the following overall composition:25.3% NH₃ (14.25 mol L⁻¹), 20.9% NH₄Cl (3.74 mol L⁻¹). A concentratedNH₂Cl solution is obtained having a titre of 1.99 mol L⁻¹ (10.2%), thatis to say a yield of 90% relative to NaOCl. That slight decrease in theyield is due to 16% of the reaction having been carried out in anon-buffered medium.

EXAMPLE III

This test was carried out using a hypochlorite solution no longer in thesupercooled state but at a temperature above its crystallisation point(+15° C.). 30 ml of a combined ammoniacal solution having titres of 12.4mol L⁻¹ for NH₃ (21.2%) and 5 mol L⁻¹ for NH₄Cl (26.8%) are introducedinto a vessel maintained at −25° C. An equivalent volume of eau deJavelle (103.8 chlorometric degrees; 4.63 mol L⁻¹) is then poured indropwise (duration of addition 15 minutes) in such a manner that thetemperature inside the reactor does not exceed −15° C. As in Example 1,the reaction medium is heterogeneous at first (partial precipitation ofNH₄Cl) and results in an NH₂Cl concentration of 2.19 mol L⁻¹ (11.3%),that is to say a yield of 94%.

EXAMPLE IV

For carrying out the preparation in a single-phase medium using eau deJavelle at +15° C. while neutralising all the HO⁻ ions, a quaternarymixture, NH₄Cl—NH₄NO₃—NH₃—H₂O, was used. The composition thereof interms of NH₃, NH₄Cl, NH₄NO₃ and H₂O is 13.14 mol L⁻¹ (22.4%), 3.02 molL⁻¹ (16.2%), 1.76 mol L⁻¹ (14.1%) and 26.2 mol L⁻¹ (47.3%),respectively. The experimental conditions are identical to Example 3.Using eau de Javelle of 98.4 chlorometric degrees (4.39 mol L⁻¹), anNH₂Cl solution is obtained having a titre of 2.01 mol L⁻¹ (yield 90%),that is to say a content in terms of weight of 10.3%.

EXAMPLE V

This test is identical to Example 4, but with all the ammonium chloridebeing replaced by ammonium nitrate. Thus, starting from eau de Javelleof 4.65 mol L⁻¹ (104.3 chlorometric degrees) and an ammoniacal mixtureof 7.55 mol L⁻¹ of NH₃ (12.9%) and 5 mol L⁻¹ of NH₄Cl (27%), the yieldof the reaction establishes itself at 95%, which corresponds to an NH₂Clsolution of 2.21 mol L⁻¹ (11.4%).

EXAMPLE VI Continuous synthesis of H.G. chloramine

The chloramine synthesis is carried out in a stirred cylindricalcontinuous reactor maintained at a temperature of from −20 to −30° C.Two lateral inlets in diametrically opposite positions allow the H.G.hypochlorite and ammoniacal solutions to be introduced continuously. Theco-reagents are cooled beforehand by circulation in two spiral coilsintegrated in two cylindrical thermostatic jackets. Their compositioncorresponds to that defined in Example 4. The flow rates in terms ofmass are pre-regulated so that the injection is equivolumetric (4ml.min⁻¹). The injection temperatures for the reagents were fixed at 15and −30° C. for NaOCl and the quaternary mixture NH₄Cl—NH₄NO₃—NH₃—H₂O,respectively. The temperature prevailing within the reaction mixture is−11° C. At the reactor outlet, an NH₂Cl solution having a titre of 2.07mol L⁻¹ (10.6%) is obtained continuously.

Synthesis of N-amino-3-azabicyclo[3.3.0]octane starting from H.G.chloramine

The solutions of hydrazine (N-amino-3-azabicyclo[3.3.0]octane) wereprepared by the action of 30 ml of NH₂Cl cooled to −15° C. on 130 g of aheteroazeotropic alkaline solution (30% 3-azabicyclo[3.3.0]octane)containing 3.8 g of sodium hydroxide. The chloramine solutions havingtitres of 2.18 and 2.21 mol L⁻¹ were synthesised according to themethods described in Examples 4 and 5, respectively. The duration of theaddition is 20 minutes and the temperature of the reaction mixture ismaintained at 60° C. Under those conditions,N-amino-3-azabicyclo[3.3.0]octane solutions having titres of 0.36 and0.365 mol L⁻¹ (4.34 and 4.42%) are obtained, that is to say a yield offrom 92 to 93% relative to NH₂Cl.

Synthesis of N-amino-2-methylindoline starting from H.G. chloramine

In the same manner, by proceeding under the conditions in patentSpecification EP 462 016, a solution of N-amino-2-methylindoline isobtained by the action of chloramine on an alcoholic solution of2-methylindoline.

What is claimed is:
 1. Process for the synthesis of high-gradechloramine solution, wherein a sodium hypochlorite solution ofapproximately 100 chlorometric degrees is reacted with a combinedmixture of ammonia and ammonium salts at a temperature of −5 to −20° C.2. Process according to claim 1, wherein continuous preparation in ahomogeneous medium is carried out with an ammoniacal combination basedon ammonium nitrate (NH₃/(NH⁺ ₄)_(α)H⁺ _(β)A^((α+β)−)/NH₄NO₃/H₂O),wherein α is 0 or 1, β is 0 or 1, and A is Cl or CO₃.
 3. Processaccording to claim 1, wherein discontinuous preparation is carried outusing a mixture of the type NH₃/(NH₄ ⁺)H⁺ _(β)A^((1+β)−)/H₂O wherein βis 0 or 1 and A is Cl, CO₃ or NO₃.
 4. Process according to claim 2;wherein the sodium hypochlorite of 100 chlorometric degrees is at atemperature higher than or equal to 15° C.
 5. Process according to claim1, wherein the ammoniacal reagent is precooled to a temperature of −20to −30° C.
 6. Process according to claim 1, wherein at least 90% of thehydroxyl ions produced by the reaction are neutralised and the pH ismaintained at 10 to
 12. 7. Process according to claim 1, wherein theratio of the reagents ([NH₃]+[NH⁺ ₄])/[ClO⁻] is from 2 to
 5. 8. Processaccording to claim 1, wherein continuous preparation in a homogeneousmedium is carried out with an ammoniacal combination based onNH₃/NH₄NO₃/H₂O or NH₃/NH₄Cl/NH₄NO₃/H₂O.
 9. Process according to claim 1,wherein discontinuous preparation is carried out using a mixture of thetype NH₃/NH₄Cl/H₂O.
 10. Process according to claim 3, wherein the sodiumhypochlorite of 100 chlorometric degrees is at a temperature higher thanor equal to 15° C.
 11. Process according to claim 1, wherein at least90% of the hydroxyl ions produced by the reaction are neutralised andthe pH is maintained at approximately 10.5.
 12. Process according toclaim 1, wherein the ratio of the reagents ([NH₃]+[NH⁺ ₄)/[ClO] is about2.7.